Field of the Invention
The present invention relates to a rear converter optical system which is detachably mounted on an image side of a main lens system to increase the focal length of the entire system, and is preferably applied to imaging apparatuses such as, for example, a silver halide film camera, a digital still camera, and a video camera.
Description of the Related Art
A rear converter optical system is conventionally known which is mounted on an image side of a main lens system, namely, an imaging optical system, to change the focal length of the entire system.
The imaging area can be easily expanded by using the rear converter optical system. Moreover, the rear converter optical system has an advantage of smaller size than a converter optical system mounted on an object side of the main lens system.
A rear converter lens is conventionally known which is mounted on the image side of a main lens system to increase the focal length of the entire system (Japanese Patent Application Laid-Open No. 2012-47869). Moreover, various imaging apparatuses including imaging elements of different picture sizes are widely used, and use their dedicated imaging optical systems. If an imaging optical system commonly usable in imaging apparatuses with imaging elements of different picture sizes can be provided, there is no need to prepare imaging optical systems dedicated to the different picture sizes and this is very convenient. There is conventionally known an imaging optical system in which a conversion optical system having a negative refractive power is detachably mounted on the image side of the main lens system to cope with imaging elements having different picture sizes (U.S. Pat. No. 6,400,515).